Footfall Noise Research Articles

A new rating method for low-frequency impact noise

Residents, building owners, architects and acoustic consultants are rightly concerned about footfall noise transmission through multi-family building floor/ceiling assemblies. By code, most projects in the USA are required to meet a minimum design rating of IIC 50; AIIC 45 if field tested. However, no matter how high the rating, residents in wood frame buildings often complain that low-frequency, or “thudding” footfall noise is a problem. Unfortunately, the IIC rating system does not evaluate impact noise at frequencies below 100 Hz. In this paper, we show that footfall noise is present at audible frequencies below 100 Hz, how this footfall noise can be replicated more objectively using ball drops or a tapping machine, and how measured impact noise might be used to develop a single number rating for low-frequency impact noise insulation of field tested floor/ceiling assemblies. The findings presented are not meant to be taken as final results, but rather a summary of progress made to-date for work that is under-development.Residents, building owners, architects and acoustic consultants are rightly concerned about footfall noise transmission through multi-family building floor/ceiling assemblies. By code, most projects in the USA are required to meet a minimum design rating of IIC 50; AIIC 45 if field tested. However, no matter how high the rating, residents in wood frame buildings often complain that low-frequency, or “thudding” footfall noise is a problem. Unfortunately, the IIC rating system does not evaluate impact noise at frequencies below 100 Hz. In this paper, we show that footfall noise is present at audible frequencies below 100 Hz, how this footfall noise can be replicated more objectively using ball drops or a tapping machine, and how measured impact noise might be used to develop a single number rating for low-frequency impact noise insulation of field tested floor/ceiling assemblies. The findings presented are not meant to be taken as final results, but rather a summary of progress made to-date for work that is...

Comparative analysis of resilient and dense materials in lightweight construction for impact sound attenuation

Resilient underlayments are commonly utilized as a primary method of reducing footfall noise in architectural acoustics. Although resiliency is a large component of a partition’s footfall performance, as well its ability to achieve higher AIIC ratings through ASTM E1007 AIIC testing, adding resiliency alone does not always address all of the frequencies which cause disturbances due to footfall. Particularly in lightweight construction, the density of the configuration is also a critical component of a successful solution. Due to the lack of sufficient mass in lightweight construction materials, successful treatment for impact noise disturbances in lightweight conditions becomes more difficult to achieve. This paper compares data with different flooring configurations in mock-up ASTM AIIC testing conditions in order to evaluate advantages and disadvantages of ANISPL (Absorption Normalized Impact Sound Pressure Level) performance in different frequencies. Resiliency and density are added in varying combinations in a wood frame construction in order to better understand their relationship to AIIC ratings and a partition’s success in impact noise insulation.

Acoustic characterization of in-room footfall noise

Existing literature concerning footfalls is primarily focused on its transmission between spaces, such as a floor/ceiling's Impact Isolation Class. Studies at the University of Hartford measured in-room sound power spectra produced by footfalls on twelve different floor surfaces using human subjects and a standard tapping machine. Within a qualified reverberation room, fourteen male and female subjects walked on the floor surfaces while wearing three different types of footwear: leather-soled shoes (hard), rubber-soled shoes (medium), and sneakers (soft). Sound power spectra and vibratory signatures were measured in 1/3 octaves according to the ISO 3741 standard. A tapping machine was also used on each floor profile using both standard drop weights and with cored samples of the same shoe soles attached to the bottom of each weight. The data for each floor profile produced averages by shoe type along with corresponding 95% confidence intervals. Correlations between sound power and vibratory spectra produced with human walkers versus tapping machine (both with and without “shoes”) were investigated, resulting in correction factors to model machine tapping as human footfalls. [Work supported by The Paul S. Veneklasen Research Foundation.]

Cultureshock Los Angeles: A midwesterner’s guide to acoustics, food trucks, and surfing

Samantha Rawlings & Joshua Magee were awarded a Student Paper Award at the Fall 2007 Acoustical Society of America conference in New Orleans for undergraduate research on sound radiation from footfall noise. This student project paved the way for Samantha to move to Los Angeles to join Veneklasen Associates, which was a wholly un-looked for opportunity for someone who once laughed outright at a Hardees commercial showing a hamburger wrapped in lettuce. Since moving to LA, Samantha has become a LEED AP and Project Manager and has had the chance to work on projects of all size and scope; everything from the “mystery noise” cold call to landmark project such as City Creek Center in Salt Lake City and Wilshire Grand in downtown Los Angeles. Additionally, Samantha has participated in research projects that have been presented at ASA, NoiseCon, and Internoise conferences. In this presentation, Samantha reflects on the surprising events of the past seven years and the adventure of learning to fit in and love Southern California.

Development of a low-frequency impact noise metric

Low frequency footfall noise (“thudding”) is a common source of complaints in lightweight joist-framed multifamily projects. Previous work by the authors has indicated that the low frequency impact sound pressure levels (LFISPL) from a standard ISO tapping machine are highly correlated with occupant reaction [LoVerde and Dong, J. Acoust. Soc. Am. 112, 2201 (2002), LoVerde and Dong, INCE Inter‐Noise 2004 Proceedings, 167 (2004)]. In order to be useful, the raw LFISPL must be translated into a single number that maintains the high correlation with subjective reaction while providing adequate dynamic range to distinguish the performance of different assemblies. Candidate metrics are evaluated.

Subjective Response to Foot-Fall Noise, Including Localization of the Source Position

Although an impact noise level is objectively evaluated the same according to current standards, a lightweight floor structure is often subjectively judged more annoying than a heavy homogeneous structure. The hypothesis of the present investigation is that the subjective judgment of impact noise is more annoying if the source position can be localized; lightweight structures have a more localized radiation than heavy structures. For the heavy structures the reverberant vibration field is dominant, therefore having a distributed radiation. A listening test is used to assess the subjective annoyance, using simulated binaural room impulse responses, with sources being a moving point source or a non-moving surface source, and rooms being a room with a reverberation time of 0.5 s or an anechoic room. The paper concludes that no strong effect of the source localization on the annoyance can be found.

Acoustic and vibratory characterization of in‐room footfall noise: Part 2.

Prior to Phase I of this study [ J. Acoust. Soc. Am. 22], existing footfall literature was primarily focused on transmission between spaces, i.e., IIC. This study measured the sound power and vibratory spectra produced by footfalls using both human subjects and standard tapping machines. One tapper had rubber‐tipped drop weights and the other had cored samples of shoe soles used by human participants. Within a reverberation room, 12 floor profiles were tested with the tapping machines. Human subjects were tested with three previously tested floors and a new floor profile. Fourteen male and female subjects walked on the floor surfaces while wearing three different types of footwear: leather‐soled shoes (hard), rubber‐soled shoes (medium), and sneakers (soft). Sound power spectra and vibratory signatures for each condition were measured using the procedures of ISO 3741. The current study verified repeatability from Phase I to Phase II, produced sound power footfall data for vinyl flooring applied directly to concrete, and developed improved correction curves to model tapping machines as human footfalls. Similarities between the rubber‐tipped tapper and women's leather shoes and a comparison of sound power and corresponding vibratory signatures are discussed. [Worked supported by The Paul S. Veneklasen Research Foundation.]

Human footsteps induced floor vibration

The generation of the impact sound by the act of the human walk involves two factors, the characters of the footfall and the shape of the induced floor deflection. The footfall noise is created by the impact excitation and the characters of the footfall depend on the foot‐ware: the heels and the frequencies of the footfall. The shape of the floor deflection depends rather on the geometrical walking pattern and the construction of the floor structure. In this investigation, the vibration patter of the light‐weight construction floor is created by the same walking object, a male with common height. The excitation from the person to the floor in the FE simulations is a function of the length of the foot and the weight of the walking object. The geometrical time history is of the foot step allows it to have different directions in the room. Since the excitation is assumed to be deterministic, differences between the excitation frequencies are estimated from the video records. The goal of this investigation is...

Acoustic characterization of in-room footfall noise

Existing literature concerning footfalls is primarily focused on its transmission between spaces, such as a floor/ceiling’s Impact Isolation Class. This study measured in-room sound power spectra produced by footfalls on eleven different floor surfaces using human subjects and a standard tapping machine. Within a reverberation room, 7 male and 7 female subjects walked on each floor while wearing 3 different types of footwear: Leather-soled with hard heels, rubber-soled with rubber heels, and sneakers. Sound power spectra were measured in 1/3 octaves using the procedures of ISO 3741. A tapping machine was also used on each floor profile using both standard drop weights and with cored samples of the same shoe soles attached to the bottom of each weight. The data for each floor profile produced averages by shoe type along with corresponding 95% confidence intervals. A total of 143 average sound power spectra were generated, based on eleven floors with thirteen averages per floor (3 male, 3 female shoes, 6 shoed tapping machines, and 1 bare tapping machine). Spectral results for each shoe/floor were studied and compared. Correlations between sound power spectra produced with human walkers versus tapping machine were investigated. [Work supported by The Paul S. Veneklasen Research Foundation.]

Assessment of low-frequency footfall noise in wood-frame multifamily construction

The impact insulation class (IIC) rating of floor/ceiling constructions fails to identify low-frequency footfall noise problems common in contemporary wood-frame multifamily construction. Because the IIC procedure ignores the impact noise spectrum below 100 Hz, the rating is not influenced by the low-frequency impact spectra produced by a typical live-walker, which usually peak in the region of 15 to 30 Hz and are associated with the ‘‘thuds’’ and ‘‘thumps’’ commonly observed. Data comparing the shape of the typical low-frequency impact noise spectrum produced by a live-walker and that of the standard ISO tapping machine indicate that the tapping machine might potentially be used as the basis for obtaining low-frequency impact noise ratings [W. E. Blazier, Jr. and R. B. DuPree, J. Acoust. Soc. Am. 96, 1521–1532 (1994)]. However, a comparison made between the two sources in the range above 100 Hz shows significant differences in the spectra produced by the tapping machine and a live-walker. This suggests that a more meaningful IIC rating of mid- to high-frequency impact noise might be obtained by cushioning the tips of the hammers in the standard ISO tapping machine, in order to better align the impact spectrum with that of a live-walker.

Investigation of low-frequency footfall noise in wood-frame, multifamily building construction

An investigation of low-frequency footfall noise in multifamily, wood-frame residential construction has led to the conclusion that, at present, there is no economically practical method of avoiding the perception of ‘‘thuds’’ and ‘‘thumps’’ in rooms beneath the walking surface. The IIC rating of a floor system is meaningless with respect to the perception of these low-frequency components of footfall noise, because the methodology ignores the frequency spectrum below 100 Hz; the peak energy in a footfall spectrum occurs at the fundamental natural frequency of the floor/ceiling system, which with typical light-weight structural framing is usually between 15 and 30 Hz. Although the construction of floated floors, or the addition of carpeting, is effective in attenuating mid- to high-frequency components of footfall noise, the data indicate that the amplitude of floor response at the natural frequency is actually increased. It is believed that this occurs because walking on a more resilient system results in a longer rise-time of the footfall waveform, which permits more low-frequency energy to be coupled into the system. The principal factor controlling the perception of low-frequency footfall noise is the point-stiffness of the structural floor system. In normal light-weight residential construction, the stiffness is usually much less than that required to avoid an audible disturbance. However, such problems are relatively rare in concrete structural floor systems, due to their substantially increased stiffness.

Comparison of Three Methods of Rating Floors for Impact Noise

About 200 floors were examined in the laboratory using as sources the ISO tapping machine and female walkers wearing hard high heels and prejudged to be consistent vigorous walkers. Data were reduced to impact noise rating (INR), for tapping machine noise [see T. J. Schultz, J. Acoust. Soc. Am. 36, 729 (1964)]; and, for walking noise, to loudness [see T. Mariner and H. W. W. Hehmann, J. Acoust. Soc. Am. 41, 206 (1967)], and to a detectability rating [see B. G. Watters, paper L3]. While loudness and detectability rating for these tests correlate generally within the estimated experimental error (±10% loudness) involved in the walking tests, there are larger discrepancies for some of the louder floors that subjective judgment had classed as “more detectable than loud” before detectability had been calculated. We conclude (1) that detectability rating is more significant than loudness rating and (2) that the INR is inadequately correlated with suppression of walking noise, whether related to loudness of footfall noise or to detectability of footfall noise.

Impact-Noise Rating of Various Floors

The impact-noise transmission characteristics of approximately 75 floors have been examined using both the standard (ISO) hammer machine and real footfall as sources of excitation. The floors include concrete and wood-base construction, isolation layers, furred construction, simple and composite surfacing of various degrees of compliance, suspended ceilings. For each floor, the recently introduced Impact-Noise Rating (INR) derived from machine data is compared with the objective loudness computed from the spectrum of noise transmitted to the room below the floor when it is walked on by young women wearing hard-heeled, high-heeled shoes. The scatter of data confirms the authors' earlier conclusion that a rating method based on the standard hammer machine does not rank-order floors with adequate precision with respect to footfall noise. Floors having the same INR generally span a factor of 4 in loudness of hard-heeled female footfall. Floors producing the same loudness of footfall noise span in excess of 10 INR numbers. Since the loudness of transmitted hard-heeled footfall is self-consistent within ±10% (or approximately one INR number on the average), the observed discrepancy is fundamental, not due to poor technique.